Doctors in Newark have diagnosed what they say is the first case of AIDS in this country that was caused by a form of the AIDS virus found mainly in Africa.

The case involves a West African who arrived in this country about a year ago. The patient told doctors at the hospital of the University of Medicine and Dentistry of New Jersey that she has had no sexual contacts since arriving here, according to one AIDS expert familiar with the case.

Federal officials had predicted the eventual appearance in the United States of the virus, known as HIV-2 to distinguish it from the chief AIDS virus, which is called HIV-1 for human immunodeficiency virus.

While there have been numerous reports of HIV-2 in the United States, there have been no cases until now in which the infection was linked to the symptoms of AIDS.

HIV-2 was found first in West Africa, then in Europe and later in Brazil. In some parts of West Africa a large fraction of the population is infected with HIV-2, while there are very few HIV-1 infections. HIV-2 had spread down the West Coast of Africa and around to one country in East Africa, as if traveling along shipping routes, one researcher reported at a recent conference on AIDS in Africa.

For the past year, researchers from the Centers for Disease Control and Food and Drug Administration have looked for the HIV-2 virus, but among some 20,000 people tested there were no cases in which a patient had HIV-2 infection alone.

The significance of the virus' appearance is unclear, researchers said. Though it apparently causes AIDS, there is some dispute about whether the disease is as severe or appears as often as that caused by the chief AIDS virus.

Dr. Luc Montagnier of the Institute Pasteur in Paris has reported numerous cases of people in Europe and Africa with AIDS symptoms who are infected only with HIV-2.

Drs. Max Essex and Phyllis Kanki at the Harvard School of Public Health, who studied HIV-2 in Senegal, have said it may cause illness less frequently than HIV-1 and that the illness it does cause may be less severe. In that West African country, a substantial percentage of the adult population is infected with HIV-2, but few have been found with AIDS symptoms, the researchers say.

"I don't think this is a cause for worry," Kanki said yesterday. "We have been expecting it to arrive. It is still a question whether it will be a cause of disease here, or how much." Whether or not it causes disease, it will probably spread among the same people now at risk, not moving into new groups.

A spokesman at the New Jersey medical school refused to give details of the HIV-2 case, which he said will be discussed at a news conference today.

If federal monitoring of the virus turns up larger and larger numbers of cases associated with disease, according to federal officials, it may be necessary to begin the routine use of another AIDS test to go along with the one now in wide use in this county.

A screening test for HIV-2 has been developed and is awaiting approval by the FDA. It is in use by researchers.